This invention relates to a wood preservative composition capable of providing improved wood preservative performance in a wide variety of applications without giving rise to any toxic problem to human beings and animals.
Wood is one of the best structural materials for the construction of buildings because of increased specific strength, ease of processing, and relatively low cost. However, wood has one serious drawback that it is susceptible to decay by wood destroying fungi or attack by wood-worms, borers and termites. To eliminate this drawback, wood was traditionally treated with preservatives such as CCA (copper-chromium-arsenic system), PF (phenol-fluoride system), creosote oil and the like by pressure impregnation or immersion. In recent years, there is the need for wood preservatives which are free of heavy metals and safe for human beings and animals and do not cause pollution as public concern is directed to environmental pollution and hygienic influence. A variety of low-toxic wood preservatives have been proposed to meet such requirements.
Wood preservative compositions comprising the sodium salt of 2-mercaptobenzothiazole were proposed by the inventors as the most promising low-toxic wood preservatives as disclosed in Japanese Patent Application Kokai-Koho Nos. 54-151102 (Nov. 28, 1979), 54-151103 (Nov. 28, 1979), and 55-108805 (Aug. 21, 1980). Another wood preservative composition comprising 2,5-dichloro-4-bromophenol or its salt is described as being safe and effective in Japanese Patent Application Kokai-Koho No. 53-26303 (1978). However, 2,5-dichloro-4-bromophenol is relatively expensive.
In general, wood preservatives are used under widely varying conditions. The results of laboratory performance tests often deviate from the results obtained when preservatives are actually applied in the field.
The inventors have researched on possible actual application of these low-toxic wood-preservatives by comparing their effectiveness with conventional preservatives such as CCA and creosote oil which are highly effective in preservation, but giving rise to hygienic and pollution problems. The inventors have found that the above-mentioned two tapes of preservative compositions may be actually used in particular applications without causing any significant problems. However, this means that these preservative compositions are not satisfactory in every application. The inventors have found that 2-mercaptozenzothiazole or its salt and 2,5-dichloro-4-bromophenol have different fungicidal spectra, are distributed in different areas when applied to wood, and exert their maximum effect at different points of time after application to wood, and that by using these two compounds in admixture, not only an additive effect is obtained where one compensates for the shortcomings of the other, as is usual with the mixing of two different fungicides, but an unexpected synergistic effect is also obtained.